This invention relates to aromatic silane compounds and to Ziegler-Natta catalyst systems which use said aromatic silane compounds as electron donors for the production of olefin polymers. The olefin polymers produced with such catalyst systems exhibit a desirable stereoblock content of from about 7 to about 25%.
Polymer stereoblock content can affect the physical properties of the polymer itself and those of products prepared therefrom, particularly films manufactured from such polyolefins and blends of such polyolefins with elastomeric materials, regardless of whether they are mechanically blended from pre-produced polyolefins and elastomeric materials or reactor blended by first producing such a polyolefin then producing the elastomeric material in the presence of the polyolefin.
Organosilane compounds have been used in catalysts (1) as an internal electron donor in a solid catalyst component comprising a halogen-containing titanium compound supported on an activated magnesium dihalide compound and (2) as an external electron donor in combination with an aluminum-alkyl co-catalyst. Typically the organosilane compounds have Si—OR, Si—OCOR or Si—NR2 groups, where R is alkyl, alkenyl, aryl, arylalkyl or cycloalkyl having 1 to 20 atoms. Such compounds are described in U.S. Pat. Nos. 4,180,636; 4,242,479; 4,347,160; 4,382,019; 4,435,550; 4,442,276; 4,473,660; 4,530,912 and 4,560,671, where they are used as internal electron donors in the solid catalyst component; and in U.S. Pat. Nos. 4,472,524, 4,522,930, 4,560,671, 4,581,342, 4,657,882 and European patent application Nos. 45976 and 45977, where they are used as external electron donors with the aluminum-alkyl co-catalyst.
Conventional propylene homopolymers, obtained by using external electron donors known in the state of the art, show a high degree of cristallinity, which determines the physical properties of the polymers, such as high melting temperature, high glass temperature and high ΔHfus. These physical properties, while necessary in some applications, are often disadvantageous in fiber and film applications, where lower bonding temperatures are required, for instance in producing laminate structures.
Hence, there is the need for external electron donor compounds which allow propylene polymers to be obtained having a relatively high degree of stereoblocks, at the same time at acceptable polymerization yields.